Such an engine type, as better described in French patent applications Nos. 2,818,324; 2,818,325 and 2,827,913 filed by the applicant, comprises at least one cylinder, a piston sliding in this cylinder, a combustion chamber delimited on one side by the upper face of the piston comprising a teat arranged in the centre of a concave bowl and at least one injection nozzle for injecting fuel with a nappe angle less than or equal to
      2    ⁢    Arc    ⁢                  ⁢    tg    ⁢                  ⁢          CD              2        ⁢        F              ,where CD is the diameter of the cylinder and F the distance between the point of origin of the fuel jets from the injection nozzle and the position of the piston corresponding to a crank angle of 50° to the top dead centre.
The fuel does thus not come into contact with the cylinder wall and it can mix with the air or the mixture of air and of recirculated exhaust gas present in the combustion chamber.
This layout, although satisfactory, involves some significant drawbacks.
Thus, in conventional combustion mode, the fuel is injected when the piston is in the vicinity of the top dead centre of the compression phase. In this situation and considering the small jet nappe angle, this fuel, in vapour-liquid two-phase form, slides along the wall of the teat, flows to the bottom of the bowl, is guided by the lateral wall of this bowl and reaches the combustion chamber. More particularly, this fuel is sent, on the one hand, to the squish zone above the piston and, on the other hand, to the centre of this bowl.
Considering the path followed by the fuel, the latter cannot easily mix with the air present in the bowl and the maximum fuel/air ratio reached for operation of the engine can remain low in relation to conventional engines using injection nozzles with a large fuel jet nappe angle, generally of the order of 140°. This results in a bad use of the air contained in the combustion chamber, notably in the squish zone.
Furthermore, the teat undergoes a high thermal stress due to the energy released during combustion and high-temperature zones are located thereon, more particularly near to the top thereof.
The present invention aims to overcome the aforementioned drawbacks by means of a fuel injection method in two stages allowing to provide suitable mixing of the fuel with the air contained in the bowl.